Many chairs which are used in a commercial environment, such as office chairs, have a height adjusting mechanism for permitting the height of the chair to be raised or lowered to accommodate the user. Typically, height adjustment mechanisms include a fluid filled cylinder, such as a pneumatic cylinder (also known in the industry as gas dampers).
Typically, office chairs comprise a wheeled base, the seat portion of the chair (which may include a chair back) and a support leg extending between the wheeled base and the seat portion. The height adjustment mechanism may employ a telescoping pneumatic cylinder which forms a part of, or may consist of, the support leg. These cylinders have a valve release pin provided thereon. The cylinder is generally in a locked condition but, when the valve release pin is depressed, the cylinder is unlocked permitting it to telescopically extend upwardly or contract downwardly.
Various control linkages for height adjustment mechanisms are known in the art. Examples of these include Kuhn et al (U.S. Pat. No. 5,069,496), Knapp (U.S. Pat. No. 4,408,800), Slabon et al (U.S. Pat. No. 4,076,308), Wirges et al (U.S. Pat. No. 4,072,288), Knoblauch et al (U.S. Pat. No. 4,373,692) and Lai (U.S. Pat. No. 5,222,783). Generally, the pneumatic cylinder is adjusted by a leaver or other mechanism which is positioned beneath the seat of the chair. Accordingly, the user must extend their arm downwardly and then transversely to a position underneath the seat to grasp the lever so that they can actuate the height adjustment mechanism. This operation tends to be difficult particularly if the chair has a large, bulky arm. Since the cylinder is only operable to adjust the height of the chair when the valve release pin is depressed, the operator must move the actuating lever to the open position and hold the lever in the open position while setting the chair in the designated height. As this may require the operator to bend or stoop over, it is difficult to set the height accurately. This is also problematic if the operator has a back problem which prevents such movement.
Nelsen (U.S. Pat. No. 4,595,237) discloses an actuating control for a seat height adjustment mechanism. The mechanism of Nelsen uses a pivotably mounted lever positioned on the bottom of the seat member. Nelson still requires the user to extend their arm downwardly beneath the seat to actuate the lever.